The present invention relates to a digital radiography system which provides a significant advance in X-ray imaging technology used for nondestructive evaluation, and is more particularly concerned with a system which will provide X-ray images having a spatial resolution and contrast resolution comparable to conventional X-ray film techniques without requiring the use of film. The system utilizes for this purpose substantially conventional, low resolution fluoroscopic equipment which, however, is modified to incorporate a specially designed multi-hole collimator plate therein, as well as digital image processing techniques.
Various methods and apparatuses have been suggested heretofore for use in examining an object by means of X-rays. One known apparatus used for this purpose is so-called fluoroscopic equipment employing an image intensifier tube which includes a thin photocathode that reacts to radiation passing through an object being examined to form an electron image which, in turn, is projected onto an output phosphor screen by means of magnetic or electrostatic focusing lenses to produce an optically visible image that can be observed directly on the output screen of the image intensifier, or which can be monitored by a video system to produce the image on a CRT display that is located in spaced relation to the image intensifier tube. Such a system has the advantage that an image of the object being examined can be obtained at low radiation dosages and in real time without the use of X-ray film. However such systems suffer the disadvantage that the image which is produced has comparatively low resolution, i.e., in the case of a conventional nine inch image intensifier system coupled to a standard 512 line TV camera, the limiting resolution which is typically obtained is substantially one line pair per millimeter (lp/mm). Such images, while useful for some purposes, have limited utility; and when it is desired to obtain a higher resolution image, the art has heretofore considered it necessary to resort to the use of X-ray film with the attendant disadvantages that such film present, i.e., cost, requirement for processing the film, etc.
The present invention obviates these problems by providing a system wherein high spatial resolution digital X-ray images can be obtained using low resolution fluoroscopic equipment, correctly modified, thereby dispensing with the need for film to obtain high resolution images. The system of the present invention can, if desired, retrofit existing conventional X-ray fluoroscopic systems and/or can be combined with existing low resolution equipment in such manner that, in one mode of operation, the equipment can be operated in conventional fluoroscopic fashion for localization purposes, i.e., to orient a test object in real time thereby to best discern a defect or to choose an optimum KV setting for the object, whereafter the equipment can be operated in a different mode to obtain a high resolution video display of the object being examined.